Telephone-exchange trunking system.



, A. E. KEITH.

TELEPHONE BXOHAVNGE TRUNKING SYSTEM. APPLIOATION FILED JULY 21, 1908.

1,078,685, I Patented Nov. 18,1913.

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I A. E. KEITH. TELEPHONE EXQHANGE TRUNKING- SYSTEM.

Patented Nov. 18, 1913.

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A. E. KEITH.

TELEPHONE EXCHANGE TRUNKI NG SYSTEM. APPLICATION rum JULY 21, 1908.

Patented Nov. 18,1913.

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jzozwei A. E. KEITH.

TELEPHONE EXCHANGE TRUNKING SYSTEM.

APPLIOATIO N I' ILED JULY 21, 1908. 1,078,685. Patented Nov. 18, 1913.

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A. E. KEITH. TELEPHONE EXCHANGE TRUNK'ING SYSTEM.

APRIGATION FILED JULY 21, 190B.

Patented Nov. 18,1913.

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ALEXANDER E, KEITH, OFHIhm-ZDALE, ILLINOIS, ASSIGNOR TO AUTOMATIC ELECTRIC COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

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Specification of Letters Patent.

Patented Nov. 18, 1313.

Application filed July 21, 1908. Serial No. 444,649.

To all whom it may concern Be it known that-I, ALEXANDER E. KEITH, a citizen bf the United States of America, and resident of Hinsdale, Dupage county, Illinois, have invented a certain new and useful Improvement in Telephone-Exchange Trunkin Systems, of which the following is a specification.

My invention relates to the automatic selection of idle trunks in a telephone er:- change system.

Priorto my invention various ways have been proposed for automatically selecting idle trunks in a telephone exchange system. For example, master switches have been em ployed which were adapted to automatically select'idle trunks ahead of the calls, so that each calling subscriber got a preselected idle trunk as soon as he removed his receiver, from the hook, or as soon as he began operating the calling dial; In'certain instances these master switches have. been provided with wipers or traveling switch members. adapted to move from one contact to-another to select idle trunks, and when the last. trunk was reached said wiper or switch member was then givena quick jump back to the first trunk or original starting point, from whence it then again traversed the various trunk terminals in the automatic selection of idle trunks. In other words, wit-h a certain class of master switches the wipers thereof had a backand fort-h movement over a row or bank of terminals corresponding to the different trunk-lines, but the automatic selection of trunks occurred only during the movement of the said wipers in one direction, and the movement in the opposite direction was merely for carrying the same back tothe first trunk or the original starting point. Furthermore, and with a certain construction of these switches, the

wipers thus operated were not lockingly connected with the actuating mechanism-that is to say, were not so connected as to be 1ncapable of moving in any other way in eX- 'act' synchronism with the said actuating mechanism, such, for example, as a ratchet and pawl mechanism. It is obvious that with such a construction as this the switch was subject to more or less unnecessary wear and tear, together with some uncertainty of operation, due very largely to the fact that after the last trunk had been seized for use it was necessary for the traveling switch member to go back to the original starting point before it could begin over again to automatically select idle trunks.

My invention contemplates, therefore, an automatic trunk-selecting switch provided with a back and forth traveling wiper adapted to select idle trunks in each direction-that is to say, a switch having a wiper or traveling contact maker adapted to have a step by-step motion in one direction to select idle. trunks, and adapted to also select idle trunks while returning in a step-by-step manner in the opposite direction. 7 It further contemplates an automatic trunk-selecting switch of this character in whioh'the ratchet and pawl mechanism for actuating the wiper or traveling. contact maker may travel constantly in one and the same direction, and inwhich means are vprovidedfor converting 'this continuous motion in one direction into a. back and forth or reciprocating motion on the part of the said wiper or traveling contact 'inaker. Again, the uniformity ,ofthe distance of travel of the wiper or contact maker, in passing from one contact to another, obtainedby giving the ratchet wheel a variable rotation-thatis to say, by roviding means for giving the ratchet whee an intermittent rotation made up of steps which are not uniform or equal in length, said steps or partial rotations varying in length according'to the extent of rotation necessary to give the wiper the de sired extent of travel, the terminals or bank contacts upon which the wipertravels being equally spaced and arranged at re 1la r in w tervals along a curved line. Th is t e wiper has a step-by-step motion in a back and forth manner, the'distancetraveledlby the Wiper between terminals being all of the same length in each direction. 7 This'uniformity of motion isobtained, as stated, by

means of a ratchet wheel thatrotates con' stantly in one direction in a step-by-step manner, the said steps vary1ng..m length,

the length of each step depending upon" the ratchet wheel is useghfor giving the wiper a step-by-ste motion at either end of said bank or row 0 terminals v Iii-this way,

I 20 more fully appear.

' as stated, a fixed or locking connection can be used between the wiper and the ratchet wheel, rather than a sliding or more or less -.loose connection, such as was heretofore can ployed. An advantage of this construction consists in the fact that the wiper operates in a step-by-step manner in each direction, selecting idle trunks in both directions, and is never under the necessity of being brought .10 back by a quick and sudden jump to starting point. Hence, there is never any jar or sudden shock during the operation of the switch, and there is consequently no danger of breakage or dislocation of the various operative parts in conjunction with which the master switch is designed to operate, or at least the possibility of such trouble is minimized. The nature and advantages of my invention will, however, hereinafter In the accompanying drawings Figure 1 is a side elevation of my improved master switch; Fig. 2 is a plan view of the master switch, showing the arm that connects the master switch with the plunger shaft, and through the medium of which the plunger shaftis operated. Fig. 3 is a perspective view of the master switch ratchet wheel associated with the plungershaft. Fig. 4 is a detail View of the master switch interrupter wheel. Fig. 5 represents diagrammatically the master switch and a line switch and the circuit connections thereof.

- Figs. 6: and 7 represent diagrammatically an established connection between a'calling substation A and a called substation A employing central station apparatus comprisingmyflimproved master switch. I v

The 'inaster switch, as shown in Fig. 1, comprises a frame 2 upon which the various operative arts are mounted, themotor magnet 3, the rgatchet wheel 4, motor magnet 5, resistancelamp 6, springs 7 and 8 and the interrupter springs 9 and 10. Also pivotally '45 mounted on the frame 2 is the motor magnet armature 11 upon the end. of which there is v, a pawl 12 that engages a tooth of the ratchet jwheel4 when the motor magnet energizes. "When the 'motor magnet 3 energizes and attracts its armature 11, the. interrupter necting link 18, which latter is in turn pivthe master switch is designed may be of the springs 9 and 10 are separated. The means; for restoring the armature 11 to normal and 139 into contact.

ment with the bank contact 39.

otally secured to the plunger shaft as a whole which comprises the members 19 and 20 (Fig. 3). This connecting link isso. arranged that when the ratchet wheel 4 is rotated in the direction indicated by the arrow in Fig. 3, the plunger shaft 19 is then given a: backward and forward motion about the shaft 20. The connecting link 18 engages a hole in the ratchet wheel 4 and at the shaft 20 is pivotally secured 'in a bracket clamp 21. At A there is shown the master switch bank comprising ten individual contacts a and one common metallic segment 22. Sliding-over these contacts in unison with the backward and forward movement of the plunger shaft 19 is the bank wiper 23 adapted to atall times maintain some one of the individual segments a in electrical connection with thecommon segment 22. Be low the master switch bank 0 there is shown a plunger 24 and a plunger arm25 in locking engagement with the plunger shaft 19.

The line switch for the control of which general character disclosed in English Patent No. 26,301 of 1906, and comprises the well-known trip magnet 26 (Fig. 5), the release magnet 27 and the bridge-cut-ofiz' relay 28. The trip magnet 26, when energized,

moves its armature 2.9 from engagement with the plunger arm 25, thereby permitting the plunger arm to move about the pivot points 30, due to the tension of the spring 31, and thrust the plunger 24 into the bank terminal Q. y I The operation of the master switch may be more clearly understood by reference to the circuit drawing in Fig. 5. In this figure the line conductors 732,.and 33 leadto the subscribers substation. When the subscriber at the substation turns the dial for the first digit the rotary line conductor 33 is momentarily grounded. This momentary grounding provides an energizing circuit for t e'trip magnet 26 extending from the substation to the line conductor 33, conductor 34, through the bridge-cut-off relay springs 35 and 36, through the winding of the trip magnet 26, conductor 37, through the motor magnet relay springs 15 and 16 to the battery lead 38, thence through battery B to ground G. The trip magnet 26, upon energizing, attracts its armature and permits the plunger 24 to engage the bank terminal Q, pressing the bank springs 40 and 41, I40 and 141, 136 and 137,'and 138 For convenience of explanation it wi V e assumed that when the plunger '24 enter (1 the bank terminal Q the master switch wiper'23was in engage- In that' event, and when the plunger 24' enters the bank terminal Q and closes the springs 40.

and 41in contact, an energizing circuit is 139 manner similar tothat of a buzzer. --niotor magnet 3 continues to operate in this manner as lon'g as the s rings 7 and 8 engage and energize the re ay 5, which latter provides theenergizingcircuit for the motor .nia'gnet 3. The motor magnet-continues toestablished through the motormagnet relay which extends from ground G the winding 42, conductor 43 to the common segment 22, through the wiper 23, individual 5 segment 39, conductor 44', through the upon energizes and presses the springs 16 and 17 into contact, which closes an ene'rgm ing circuit. through the motor magnet 3, said circuit extending from ground Gr through the winding of the motor magnet 3, interrupter springs and 9, con'ductor 45,,motor magnet'relay springs 17 and-16 to the battery lead 38, thence through battery B to ground G. The motor magnet, upon energizing, attracts its armature 11. The pawl 12 engages a tooth of the ratchet wheel :4:

and moves the latter one step. When this occurs the spr ng 8 engages the spring 7 (bearing in mind that the spring. 7, prior to this operation, engages a notch46 of the toothed wheel-.14), and when the ratchet [wheel 4 is given one step the spring 8 slides off from the top of the notch and engages thespring 7. \Vhen this occurs a new energizing circuit is provided for the winding 1 42 of the relay 5, said circuit extending from ground G through the winding 42, springs 7 and 8, resistance lamp 6 to thebattery lead 38, thence through battery B to-grou'nd G.

Furthermore, the motor magnet, when energized, separates the interrupter springs .9'

and 10, thereby breaking its own circuit in a operate, rotating the, ratchet Wheel in a clockwise direction (Fig; 5) until the springs 7 and 8 engage the notch 47. When occurs the spring '7 passes out ohm;

gagement with the s ring 8,.thereby-opening the circuit throng 1 the winding 42. The

relay 5 deenergizes, and the spring '16 returns to normalposit-ion'in engagement with.

the spring 15, thereby'breaking the energizing circuit for the motor magnet-3; When the notch 47 is rotated to the position shown in Fig. 5 the wiper 23 is rotated to the individual segment 48-that is, the notchi47 corresponds to the segment 48 in the same manner in which the notch 46' corresponds to the segment .39; also, the'notch' 49 Teornesponds to the segment 50. It will be seen that the spaces between the notches 46' andthrough The 47, and 47 and 49 are not equal, although the distances between the segments 39 and 48, and 48 and 50 are equal. This arises from the fact that when the wiper 23 occupies the first contact 39 the connecting link 18 is at the limit of its motion, anda greater rotary motion of the ratchet wheel 4 isrequired to move the wiper 23 the same distance than is required when the wiper 23 occupies some central contacta in the bank O anclthe connecting link 18 occupies some central posit-ion in this machine. Suppose, however, that when the wiper 23 engages a contact 48 a guarding potent-ial is present.

In that event an energizing circuit is closed through-the motor magnet relay 5 which extends from the contact 48 through the wiper 23, common segment 22, through the winding 42 to ground G in the same manner as previously traced, The motorfmaguet'relay.1 5

5again energizes and closes the ilr'tuitator the motor mag et 3'. 'lhe niotor magnet 3 operates as before, and the wiper 23 is carriedto the next contact 50 and'the springs 7 and "8 to the tooth 49 of the wheel 14. It will be understood, of course, that when the relay magnet operates and moves. the connecting link 18 from one positionto another, the plunger shaft 19 and all plungers 24 which are in-locking engagement with -tl1e 1 said shaft are moved-toanew position opposite an idle terminalsiuiilar t0. the terminali Q. W hen, the bank renne -a o isr-engaged .by the plunger 24,}as previously expla1ned,

the subscrlbersline-conductors 82 and'33 1 1 are extended to-th'e trunk. conductors 51 and? 52 which, lead to'ja selectorswitchj'ofthei general -type' d1sclosed in United States Letters Patent N0.f81 5,321;, granted March 13,

1906," to Keith, EricksonandErickson. The

selector's'witeh is in t finada-pted to make connection with-the connect-or, which may-in turn be operated by the subscriber to estab lish connection ,With any subscribers line in the desired group, as is-we ll known. :Itwill be understood that the plunger shaft 19 may control a group of plungers, and that when .any' line switch is operated to seize a trunkline an energizing circuit is established through-the motor .magnet-relay 5 in the manner previously, ,explaind, and the master switch-operatesto carry the idle plun- 'gers opposite the next bank segment. If a multiple of thisbank segment is engaged a guarding potential is established at the cor- 1 o responding segment of the master switch,

and the motor magnet relay again energizes and closes the circuit through the motor magnet. This c ues as long as theiviper 23 engages bank contacts upon which there p is a guarding potential.

Referrin to Fig. 6 it will be seen that the substation A is somewhat di'fi'erentfrom the usual automatic substation, said -substation A. being arranged and modified to 45 the wipers-7 operate in connection with a two-wire system' that is, with a system in. which no 57, transmitter 58, condenser '59, ringer 60,-

impulse wheel 61 which has the usual im 10 pulse teeth 62. 'The impulsewheel is $65- cured to the shaft 63 which is also secured to the dial (not shown). When the dial is turned the impulse teeth 62 are adapted to engage the cam 04: upon the end of. the spring 65, thereby carrying the latter out of engagement with the spring 66. Upon the switch-hook 541 there is a cam 67 which, when the switch-hook is up, permits the springs 68 and 69 to engage, thereby bridg ing across the subscribers line conductors 32 and 33 the primarycircuit'including the transmitter 5-8 in series with the primary winding 56; but when the'switch-hook is down the spring 68 is carried out of engage- 25,ment with the spring 69 and into engagement with the spring v70, whereby the ringer '60 in series with thecondenser 59 is bridged across the line conductors32 and 33. Thefirst-selector switch shown, at E is of the cut, and, as .shown,' is modifiedto adapt it to. operate in 00111180131011,\Vlth'fiftWO-W11e sysgeneraltypedescribedin. said selector pat.-

" tern. Among otherdetailsit-embodies the a followingfeatures: The switchshaft (not J's'hown); carries the vVerticaland rotary' wip r- 111 and 72,xrespectively,,and .a priyatewiper' 73. A The .side. switch is well lmown and comprises} the side switchf wipers 74,37 (6 and 7 7- whickmay be designate oiasliith ertical, may nnd private side switch" er eand'tha rotary magnet wiper,

r'e'spec 'lvelyi; The side 1jswitch-"1s under the" 'cofitrhlg of thefprivate magnet, 78, 'ahdQwhen the side switch isjnnormalpr first psit-ion 4- 75Z'761and'77-{occupy'the co tact j'points 3180, 81 82, respectivly.

' In second position 'gthe'tlwipers "rest; on; the contact points. 83 ,"8 i, '85 8'6; respectirfely,

. and when; in .third position' the contact point spective wipers; Tirewmdmgs-ofthe usual vertical and 'rotar; ne' clays Tare. in this e' d i h 0x15d ub -w i e ay 91 comprising thel winding 92'whi1ch'is con nected with the battery-' leald 38 and? also. withthe vertical trunk conductor when the,

the side switchis in first position, the sub-.

scriber controls the vertical magnet 94 which 55 operates to raise the shaft and wipers 72 and 73 vertically. The line relay 81 also con-. trols the private magnet relay 95,. which lat ter in turn controls the private magnet 7 8. As usual the private magnet controls the side switch. W'hile the side switchis in second position the rotary magnet 96, which operates to carry the switch shaft wipers 71, 72 and '73 in a rotary direction, is energized. The release magnet 97 p ovides means for restor ing the selector SW1 h to normal position.

Upon the switch shaft which c arries the shaft wipers 71, 72 and 73 there is mounted the arm 98 whi h, when the shaft is raised one or more StfitDS, permits the spring 99 to engage the contact point 100, whereby the 9' release magnet 97 is connected to the battery lead. Therelease relay 101 is provided'for closing the energizing circuit at the release magnet 97 after the switch is operated. -The rela ys 101 and 95 are slow- 35 acting relays-that they are so'provided with a copper shield'that wh n energized, and the energizing circ'aii the broken, said relays remain in. anope ated position'for a moment orso. In other words, they do not instantly return to normal position after the energizing circuit'is broken.

' The connector switch H is a modified form -of the connector switch disclosed in United States Letters Patent No. 815,176, granted March 113, 1906," to Keith, Erickson and Erickson- The connector switch shaft (not shown) ,like the-switch shaft of the selector, carries the line wipers 102 and 103 and a .pri'vate wiper 104. The connector switch is 1 also controlled by the calling subscriber through the medium of adouble-wound line trelay 105. The'line relay 105 is provided d giwith the windings 1, 06 and 107. One terminal of the windin' 106 is connected to 105 the-battery. lead, while the other terminal 'is connected with the vertical trunk line conductorg The winding 107 is connected with ground and also with the-rotary trunk-line conductor. This.line relay.'l05.directly con- 4 trols the vertical, magnet=108.1 The funct in of the vertical ,inagnet [108 is to give the shaft and shaft wipers a ertical motion, and the rotary magnet 109 imparts to the shaft and shaft wipers a rotary or circular Emotion. 'The connector switch is also pro :videdwith the'slow-acting release relay 110,3

which is the same as the release relay 101 of -the=first-sel ector switch. As usual, the private, magnet relay 111 controls the private 1-20 magnet 112.1 which latter controls the side switch wipers113, 114,115, 116 and 117.

The "back-.l ridge. relay 118, comprising the windings 1'19 and 120, provides the means whereby the called subscriber is furnished 12% withbattery current for talking purposes.

As here shown, the connector switch is of the automatic ringing types-that is, a signaling of the called subscrihen is-- not dependent upon the calling subscriber pressing a signaling button when he calls a line not.

his own; for as soon as connection is established with the desired line the interrupter 121 intermittently closes an energizing circuit through the ringer relay 122, whereby the terminals of the ringer generator I are intermittently bridged across the normal conductors of the called line.

The relay 123 is so arranged that if a busy line is called the connector side switch is locked in second position, and the calling subscriber is given the busy-signal. The means whereby the connector switch may be restored to normal position is provided-by the usual release magnet 124 which, when the connector switch shaft is raised one or more steps, is

connected to the battery lead through the normal springs 125 and 126. By means of the condensers 127 and 128 the circuit through the connector switch is divided into two sections.

. The busy-signaling apparatus J comprises the interrupter 129 in series with the wind- .ing 130 of the induction-coil 131.

The winding 132 is connected with the spring 133, and when the relay 123 energizes, the busysignaling apparatus is connected with the connector side switch wiper 113,

It will be assumed that the subscriber at substation A wishes to call a subscriber at substation A (Fig. 7), to which latter substation is allotted the number 220. To call the, number 220 the subscriber at substation A (Fig 6) removes his receiver from the switch-hook and operates the calling device for each digit in a well-known mannerthat is, when the receiver is removed from the switch-hook a preliminary impulse provides an energizing circuit for the trip magnet 26 ofthe line switch C, whereby the said line switch C is operated to seize a ireselected idle trunk-line leadin to the rstselector switch E. The dial 1s turned for the first digit 2, and upon returning to normal position operates the first-selector switch to establish connection with an idle trunk-line leading to a connector switch H (Fig. 7 The impulses delivered by the dial for the last two digits are directed toward the connector H, which latter operates to place the shaft wipers in connection with the contacts corresponding to the desired substation. The primary impulse for energizing the trip magnet 26 occurs when the receiver 53 is removed from the switchhook 54, and the cam arm 67 permits the spring 68 to engage the spring 69, thereby removing the ringer from across the line and bridging the primary circuit instead. When the primary circuit is thus bridged across the line the energizing circuit for the trip magnet 26 is completed and extends from ground G through the springs 134 Y and 135 to the line conductor'32, throutgh .the primary circuit at the substation to e line conductor 33, through the bridgecub otf springs 35 and 36, trip magnet 26, com ductor 37, through the springs 15 and- 16 to the battery lead 38, thence through battery '13 to ground G. As soon as .the trip'magnet 23. energizes, its armature is attracted and the plunger is thnust into the'bankterminal Q. When the plunger engages the" bank terminalan energizing circuit is established throughlthe motor magnet relay 5, which in turn operates to close an energizing circuit-= through the motor magnet 3 of the master switch D. The motor magnet then operates to advance all idle plungers that. are in I locking engagement with the shaft- 19 to. a point opposite the next idle-bank terminal similar to the terminal just engaged. The circuit through the relay 5 extends from ground G through the winding42' of the 'relay 5 to the common segment22, wiper 23' to the individual segment 39, conductor 14, throughthe bank springs 40 and 41, release magnet 27 to the battery lead 38 thence through battery B to ground (5%..v The relay 5, upon energizing, operates to place the springs 16 and 17 is engagement, forming a circuit to the battery lead 38, thence through battery B to ground G. The motor magnet then operates, as previously explamed, to advance the shaft and the engaging plungers opposite the next idle trunk-line. At the instant that the plunger enters the bank terminal the following springs are pressed intocontact: 136 and 137,138 and 139, 140 and 1.41, and 40 and 41. The engagement of the springs 140 and 141 closes a circuit through the bridge-cutofl? relay 28 extending from ground G through-the springs140 and 141, through the winding of the bridge-cut-ofl relay 28 to the battery lead'38, thence through battery B to ground G. Said relay, upon energizing, operates to carry'the springs 135 and 35 out of engagement with the springs 134 and 36, respectively. \Vhen these springs disengage, the line conductors 32 to making a call, The subscriber thus operates the line switch 0 toestablish connection with the selector switch E, whlch latter station A removes his receiver preparatory is now operated by the impulses that arev delivered when the dial returns to normal position for the first digit, When the subscribers line conductors 32 and 33 are thus extended to the selector switch E, an energizing circuit is established through the line relay 91, said circuit extending from ground G through the winding 93, side switch wiper 75,- trunk conductor 52, bank springs, inc conductor 33, through the substation primary circuit to the line conductor 32, through the bank springs and trunk-line conductor 51, side switch wiper 74, through the Winding 92 to the battery lead 38, thence through battery B to ground G. The relay 91, upon energizing, operates to place the springs 143 and 144 in contact, whereby an energizing circuit is established through the release relay 101 extending from ground G through the springs 144 and 143, through the winding of the relay 101 to the battery lead 38, thence through battery B to ground G. The relay'lOl, upon energizing, carries the spring 145 out of engagement with the spring 146 and into engagement with the spring 147. This iis the condition of the first-selector switch E when the subscriber operates the (hit 1 for the first digit. -The first digit being 2,- the impulse spring 65 is thus carried out" of engagement with the impulse spring 66. As a result the energizing circuit through the line relay 91 is broken twice, and the spring 143 comes into contact with the spring 148 twice. Aiter the two impulses are thus transmitted, the line *relay 91 again energizes and carries the spring 143 into contact with the spring 144. As previously explained, the relay 101 is sloW-acting-that is,- slow'to deenergize, and when this energizing circuit is momentarily broken during the vertical impulses just delivered, the said relay does not deenergize, but remains in an operated position with the spring 145 in engagement with the spring 147. WVhen the spring 143 engages the spring 148 twice two impulses are transmitted to the vertical magnet 94 from ground Gr through the springs 143 and 148,

springs 145 and 147, through the private magnet relay 95, through the vertical magnet 94, side switch wiper 77 to the battery lead 38, thence through battery 13 to ground G, The impulses being transmitted, the vertical magnet 94 is thereby energized twice, and the shaft wipers are given two vertical steps in the well-known manner. It will be. seen that the private magnet relay 95 is included in the energizing circuit of the vertical magnet 94. This relay also energizes, but being a slow-acting relay it onergizes on the first im ulse and remains so until all the impulses are transmitted. This relay, upon energizing, operates to close the springs 149 and 150 in contact, whereby an energizing circuit is established through the private magnet- 78 extending from ground G through the springs 149 and 150, prlvate magnet 78 to the battery lead 38, thence through battery B to ground G. The private magnet relay 95 denergizes for the last impulse, since this energizing circuit is no longer extended after the springs 145 and 148 disengage; hence the said relay deenergizes, permitting the springs 149 and 150 to disengage, whereby the energizing circuit through the private magnet 78 is in turn broken. The private magnet now deenergizes and permits the side switch to pass from first to second position, whereby the I side switch wipers 76 .and 77 engage the contact points and 86, respectively.

The closure of contact between the side switch wiper77 and the contact point 86 sets up an energizing circuit for the rotary magnet from ground G through the interrupter springs and winding ofthe rotary magnet. 96, contact point 86, side switch wiper 77 to the battery lead 38, thence through battery B to ground G. The said rotary magnet then operates to rotate the shaft wipers 71, 72 and 73 of the selector E- into engagement with the first contact of the second level of the select-or banks, from which contact it is assumed that the trunkline conductors 151, 152 and 153 lead to the connector switch If the first trunk-line is busy, however, and the wipers have to pass over busy trunk-lines, then as soon as the private wiper 73 engages the first private bank contact the private magnet 78 again energizes, locking the side switch in second position. The energizing circuit for the private magnet extends from the grounded terminal G at the battery B through an occupying switch (not shown), through the private wiper 73, thence through the conductor 154 to the side switch wiper 76, contact point 85, through the winding of the private magnet 78 to the battery lead 38, hence through battery B to ground G. The private magnet, upon thus becoming energized, locksthe side switch wiper 77 in engagement with the 1 contact point 86, whereby the rotary maguet'96 will be energized step by step until the wipers are carried beyond the last busy contact. The instant that the private wiper reaches the-last busy contact point the energizing circuit through the private magnet 78 -braces are thus extended to the connector H an energizing circuit is established through the line relay 105 in the same manner in which the energizing vcircuit was established through the line relay 91 of the first-selector E when'the subscribers line conductors 32 and 33 were extended through the switch bank to the trunk conductors 51 and 52. Therelay 105, upon energizing, operates to shift the spring 155 out of engagement with the spring 156 and into engagement with the spring 157. When the springs 155 and 157 engage,-an energizing circuit is thereby established through the release relay 110. This circuit extends from ground Gr through the springs 155 and 157, through the winding ofthe release relay 110 to the battery lead 38, thence through battery B to ground G. The relay, upon energizing, operates to shift the spring 158 out of engagement with the spring 159 and into engagement with the spring 160; also, the

spring 161 is pressed into contact with the spring 162. This operation of the connector switch H occurs at the instant that the side switch wipers 74 and 75 of the selector switch E pass to third position andextend the subscribers line conductors 32 and 33 to the connector switch' H; The engagement of the springs 161 and 162 establishes a guarding potential for protecting the trunkline conductors 151, 152 and 153 against seizure by another selector switch. potential extends from ground G to the side switch wiper 115, springs 161 and 162 to the private conductor 153, thence to the multiple contactsof the first-selector banks. The opthrough the winding of the vertical magnet 1108, side switchwiper 116, through the winding of the private magnet relay 111 to the battery lead 38; thence through battery B to ground The private magnet relay .111 energizes when the first impulse is delivered, and since, the said relay is slowacting it remains in-ari operated position i this '-guard1ng potentialprevent other conuntil all the vertical impulses are sent. The vertical magnet, upon being energized, operates one'step at a time to carry the shaft'wipers 102, 103 and 104 two steps to a point opposite the second level. The private magnet relay 111, upon energizing, shifts the spring 163 out of engagement with the spring 164- and into engagement with the spring 165; also, the s ring 166 is carried out of engagement wit the spring 165:

This

energizing circuit is established through the private-magnet 112 from ground G through the springs 165 and 163, winding of the private magnet 112 to the battery lead 38-,

relay 111 being a. slow-acting relay, 'asiei'zplained, remains in an operated position line relay 105 returns to its operatedposicomes broken, thus permitting the-springs magnet d eenergizes, permitting tl1 e' "side switch to pass from first to second position, The calling subscriber now operates the calltransmitting ten impulses and operating the line relay 105 ten times. Each time that the The rotary magnet 109 then operates to rotate the shaft wipers into engagement with the desired line #220. As soon as-the line relay 105 ceases to operate for the-last digitthe private magnet relay lll deefnergi'zes, as explained," but in this instance permitting the side switch to trip. to third position.

spective contact points in the third position. When the side switch wiper117 engages-its third-position contact-point a guarding potential is e'stablishedat' the-private wiper 104 for protecting the seized line from outside interference while the connection is established. This guarding potential extends from" ground Gr through the side switch wiper 117', locking relay springs-169 "and 17 0 tothe private wiper 104:. Not only does nectors from seizingthe samelineov er multhe cut-off relay 174 of the line.--'switc C'. Of course, when the side switch wipers 113 and 11 1 engage their third-position contact points, the calling suhscriberls'line is'tlen placed in'connection with the called sub s'c'iibefls'flme over .the heavy conductors When the springs 163 and i65-engagefan thence through battery B to ground fii flhe" while the vertical impulsesiare being sent but after all the impulses are delivered *the tion. The circuit through the relay 111 be? engage, the circuit through the private mag net 112 becomes broken, whereby the'jsaidl The' result. is'that the side switch"wipers 113, 1 14, 115, 116 and 117 engage tl1eir"re--- tiples of the normal 'conductois, 1.'r1, 172 and, 17 3, but it also provides means forener 'zmg .i

163 and 166 to resume their normal posi tions. lVhen the springs 163 and 165jdis-s' line relay springs 155 and 156 engage, an"

'taining the private magnet energized also; 1

85 ing device. for the last digit 0, thereby shown passing through the ringer relay springs 175 and 176 on one-side and 177' andlZS on the other. As soonlas connection is thus establis ed the ringer'r'elay 122. is

energized over he circuit established when the side-switch! w/iper 11,6'engagedits third-I positioncontactpoint. The ener'gizingcurrent flows from ground G through, the interru ter 121,'sprin'gs 179 and 180, ringer of the ringer relay 122 willbe broken peri-.

oclically so as not to ring the called subscriber continuously. As a result ringing current'is sent over the called line for energizing the bell 181. However, as soon as the called subscriber answers, the backbridge relay 118 is energized by a flow of current from ground G through the wind? ing 120, through the ringer relay springs 178 and 177, shaft wiper-.103, normal conductor 172, line conductor 182, through the [substation springs 183 and 184, thence :through the primary circuit of the substation'A to thefline' conductor 185, normal conductor 171, shaft wiper-102, ringer re- .30

lay springs 175 and 176, through the wind -119'of'the relay 118 to the battery lead I I38,""thence through battery B to ground G. "l -Vixen the back-bridge 'relay 118 is once the energizing circuit forthe :rin'ger relay 122 is interrupted at a point ibtweenth e springs 179 and 180, thus mak- -ing it impossible for the .ringer relay to energize as long as the called subscriber is on the line. 40

The two substations being ethu's connected, the subscribers may com- --municateover the conductors indicated by the heavy lines in Figs. 6 a11d7.

After the subscribers are through talking,

v between the springs 68 and69, thereby initi-' 1 :8 and 159, and 155 and 1.56, and a flow',

if the-calling. subscriber hangs up his receiverhe opens the line circuit at a point ating the release of all the switches. This release isas follows: At the instant that the circuit is broken between the springs 68 and 69 the double-wound line relay 105 and the release relay 1160f the connector H deenergize. When the slow-acting release relay 110 and the line relay 105 deenergize, the energizing circuit for the release magnet 124 is'clcsed at a point between the springs of current is therefore set up from ground G through the springs 155 and 156, springs 158 and 159, through the winding ofthe release magnet 124, normal springs 125 and,

126 to the battery lead 38,-,thbnce through battery-'1 to ground G. The release magnet instantly releases the connector switch and the side switch, thereby breaking the energizing circuit through the back-bridge relay ma-rapes 1 18 ifthe called subscriber has not in the meantime restored his receiver, and also the energizing circuit through the bridgccut-oii relay 174 of the called line switch C. As soon as the connector switch shaft reaches its lowest position it breaks the circuitfor the release magnet 124 by separating the normal springs 125 and 126, at which instant the release. magnet of'the connector is also restored, The operation of the line relay 105 and the slow-acting release relay 110 not 'only causes the release of the connector, as described, but also the release of the firstselector switch E, because the ground connection with the private conductor 153 is also removed, and thus an energizing circuit is no longer maintained for the release relay 101 of the selector switch E. This relay 101 then deenergizes and places the springs 145 and 146 in contact, whereby a circuit is completed through the release magnet 97, said circuit extending from round Gr through the springs 143 and 148, through the release magnet 97, normal springs 110 and 99 to the battery lead 38, thence through battery B and to ground G. The release relay 101 for the selector switch E is dependent upon a ground fromnthe switch. ahead to maintain it in an energized position, and hence when this ground is removed the relay deenergizes. The release magnet 97, upon energizing, places the springs 186 and 187 in contact, whereby a circuit is closed through the release magnet 27 of the line switch C. This circuit extends from ground G through the release magnet springs 186 and 187, conductor 53*, bank springs 40 and 41, through the release magnet 27 to the battery lead 38, thence through battery B to ground G. The firstselector switch shaft, -u'pon restoration to normal position, separates the normal springs 99' and 100, thereby destroying the energizing circuit of the magnet 27 of the line switch C. The line switch C returns to normal position, and. the bank springs are' separated, thus preventing any other action from the trunk After the switches are thus restored the calling subscriber may, of course, then proceed to make another call. It will be understood that the subscriber, at

substation A may call a subscriber at substation A, and that any subscriber in the exchange may call any other subscriber of the exchange'in a similar manner.

From the foregoing it will be seen that I provide an automatic trunk-selecting switch wherein the wiper or traveling contact maker is never under the necessity of being brought back by a iump or sudden movement to starting point. For this reason the operation of the switch is never subject to a sudden jar or concussion, which was heretofore thecase with certain kinds of apparatus, and hence the plungers on the shaft are not liable o be disturbed or thrown out of proper position. Also, the wear and tear on the switch is greatly reduced, as well as danger of breakage thereof, and the same is made to work smoothly and evenly, and the motion of the wiper or contact maker in both directions is made use of in the antoinatic selection of idle trunks.. The said wiper or contact maker has, it will he -seen, a uniform distance of travel in each; rection-that is to say, the distancestrom' one contact to flllOtllQl are all of uniform length, and this is produced by a variable rotation on the part of the ratchet wheel, some for-- ward steps of the ratchet wheel beinglonger than others, de iending upon the'position of the ratchet wheel at the timeth'e step is taken, and upon the position of the wiper or contact maker relative to the bank or row of trunk terminals. If the wiper is at the middle of the said bank 01"- terminals, then the minimum motion is given the ratchet wheel, because at this time the wheel 18 i moving directly; forward in a ho 'inonta plane. However, when the wiper or contact steps varying in number according to the. position oft-he wiper on the bank. It the wiper is moving from one middle contact to another in the bank the movement at this time is composed of only a few short steps forward. If, however, the wiper is moving into engagement with one of the end contacts in the bank, then the step forward from one contact to another is made up of agreater number of short steps, because in such case a larger number of the teeth on the ratchet wheel 4 will be successively engaged in order to accomplish the desired extent of movement on the part of the wiper. With the arrangement employed, therefore, the wiper has a uniform distance of travel from one terminal to the other, but has a variable or non uniform step-by-ste-p motion between terminals-that is tosay, the wiper does not'always travel at the same speed, because from one middle contact to another it moves comparatively fast, while from one end contact to another it moves much slower, the motion in the first-case being made up of a small number of relatively long steps. while the motion in the second case is made up of a greater number of relatively short steps. The result, however, as explained. is simply this, namely that the travel of the wiper from one contact to an other 18 unit-orm as far as distance 18 concerned, whereas the travel of the ratchet wheel is uniform as to speed but non-uniform or variable as far as distance is concerned. This being the case, a fixed or looking connection can be employed between the wiper and the ratchet wheel-that is to say, a connection which engages the ratchet wheel at a fixed point, and whereby the wiper must always move when the ratchet wheel moves, regardless of the, position of. said wiper relative to the ratchet wheel. This, as stated, insures a smooth and uniform mode of operation on the part of the switch, the mechanism always operating without shock or jar, and the automatic sclection of idle trunks being accomplished in an improved and exceedingly satisfactory and highly etii'cient manner. With respect to the combination of this master switch with subscribers line switches of the character herein disclosed, it will be seen that such combination results in the provision of a line switch having a new mode of operation. Previously the said line switch was provided with plungers which had a step-by-step movement in one direction, but a quick jump, or long sweep in the opposite direction. Now, however, the subscribers line switches have plungers which have a step-by-step progressive movement in one direction, and a similar step-by-step progressive movement in the opposite direction, whereby both directions of movement are utilized to bring the plungers from one trunk to another, and thus the operation of the plungers is smooth and uniform in each direction. In this way the line switches operate without shock or jar, and with less wear and tear and uncertainty of operation than heretofore. With further respect to the mode of connecting the master switch with the shaft for the plungers ot' the line switches, it will be seen that thisprecludes the possibility of the pluagsrs moving independently of the uiaSterQswIitcli-Ahat is to say, tends to prevent theg jvlungers from running ahead, so to spcalqo't the motion of the master switch. In certain previous con-- structions it was found that the pluugers had a tendency to swing past the desired position in frontl of a trunk-line terminal when given. a step forward by the master switch, owing to the momentum of the mechanism. Vith my improved arrangement, however, it will be seen that the plungers are so connected with the master switch that they will always travel to and stop exactly in front of the trunk terminals, inasmuch as the. momentum cannot carry the plungers and their shaft any farther after the master switch stops moving.- Thus the construction has another distinct advantage, namely that the plungcrs of the line switches have no surplus or excess of movement in traveling from one trunk to another, the movement of the plungers that are in engagement with the shaft ceasing instantly upon the cessation of movement on the part of the master switch.

While I have illustrated one particular form of my invention, it will be understood that I do not wish to be limited to such exact structure. Furthermore, certain of the broad features shown herein are not claimed in this application, but are claimed in a co-pending application of mine, Serial No. 311,327, filed April 12th, 1906, to which this application is subordinate.

What I. claim as my invention is 1. In a telephone system, a set of trunklines, a set of terminals corresponding to said-trunk-lines, a wiper mounted to engage said terminals, mechanism for causing said wiper to have a back and forth. motion and 'step-by-step movement over said terminals in both directions of motion thereof and means for including said trunk lines in talking circuits.

. 2. In a telephone system, a set of trunklines, a series of terminals corresponding to said trunk-lines, a wiper adjacent'said terminals, means for moving' said wiper back and forth over said terminals, and means i'ng circuits.

4. In a telephone system, a set of trunklines, a series of terminals corresponding to said trunk-lines, a wiper adjacent said terminals, a shaft upon which said wiper is mounted, anarmcarried by said shaft and pivoted thereon to swing about an axis at right-angles to that of the shaft, a ratchet wheel engaging the free end of said arm to move the same in a circle, a pawl for actuating said ratchet wheel, and means for varying the number of teeth on the ratchet wheel engaged said pawl in actuating the same to move the wiper from one terminal to iihother.

-5.'In a telephone'system, a set of trunklines, terminals corresponding to said trunklines, a shaft provided with a wiper adapted..

to engage said ter minals, an arm pivgted'iin said shaft to swing about an axis at rightangles to the'axis of'the shaft, a ratchet I wheel engaging the free end of said arm to move the same in a circle, and to thereby move the said wiper back and forth over 6. In a telephone system, set of trunk lines, bank-terminals for said trunk-lines, a plunger adapted to travel back and forth in front of said terminals, and means for giving said plunger a variable number of I steps between different terminals.

T. In a telephone system, a plurality of trunk-lines, terminals for said trunk-lines, a traveling'member adapted to move back and forth in front of said terminals, mechanism' for giving the said member a step-by-step motion consisting of a series of successive steps of variable lengths,and means for including said trunk lines in talking circuits.

8. In a telephone system, a plurality of trunk-lines, an automatic switch for seizing idle trunk-lines, automatic mechanism whereby a switching element. of said switch is given a variable speed step-by-step motion, and means for including said lrunk lines in talking circuits.

9. In a telephone system, a plurality of trunk-lines, terminals corresponding to said trunk-lines, said terminals beiii'gguniformly spaced apart, a traveling member adapted to cooperate with said terminals, having a uniform distance of travel from one terminal to another throughout the range of travel thereof, and mechanism for giving said traveling member a variable step-bystcp motion between the different terminals.

10. In a telephone system, a plurality of trunk-lines, terminals corresponding to said lines, a wiper engaging and traveling along said terminals, mechanism for giving said wiper a. variable speed step-by-step motion, and means for includingsaid trunk lines in talking circuits." I 11. Ina telephone system, a plurality of trunk-dines, .terminalsfor "said trunk-lines, a circuit-closing plunger adapted to travel 'along in frOnt' of said terminals, normally out of conlt act therewith, and mechanism for giving sai kplunger a variable step-hy-step nnot-ion bet. .:,en the different terminals.

In a telephone system, a set of trunklines, a set of; terminals corresponding to said trunlclines, a wiper mounted to engage 'said terminals, mechanism for causing said wiper to have a back and forth motion and step-by-step movement over said terminals in both directions of motion thereof, metal lic line circuits, and means for controlling the aforesaid operative elements over said metallic line circuits. I

13. In a telephone system, a set of trunklines, a series of terminals corresponding to said trunk-lines, a wiper adjacent said terminals, means for moving said wiper back and forth over said terminals, means for causing said wiper to stop on idle terminals corresponding to trunk-ln1es in each direc-'- tion of motion thereof, metallicline circuits, and means for controlling the aforesaid operative elements over saidjmetallic line circuits. p

14. In a telephone system, a so lines, a set of terminals correspo minals, mechanism for moving "the wiper from one terminal to another, adapted to give the wiper avariable number of steps between terminals, but a uniform distance of travel from one'terminal to another, metallic line circuits, and means for controlling the aforesaid operative elements over said metallic line circuits.

15. In a telephone system, a set of.tru11klines, a series of terminals corresponding to said trunk-lines, a wiper adjacent said termurals, a shaftupon which said wlper is mounted, an arm carried by said shaft and pivoted thereon to swing about an axis at right-angles to that of the shaft, a ratchet wheel engaging the free end of said arm to move the same in a circle, a. pawl for actuatmg said, ratchet. wheel, means for varying the number of teeth on the ratchet wheel engaged by said pawl in actuating the same to move the wiper from one terminal to-another, metallic line circuits, and means for controlling the aforesaid operative elements over said metallic line circuits.

16. In a telephone system, a set of trunklines, terminals corresponding to said trunklines, a shaft provided with a wiper adapted to engage said terminals, an arm pivoted on said shaft to swing about anaxis at right angles to the axis of 'the shaft, a ratchet wheel engaging the free end of said arm to move the same in a circle, and to therebymove the said Wiper back and forth over.

said terminals, a pawl engaging said ratchet wheel to actuate the same, a notched wheel rotating with the said ratchet wheel, provided with notches at irregular intervals in .the periphery thereof, a magnet for operat ing said pawl, means including circuit contacts engaging the periphery of said notched wheel to control the action of said magnet and pawl, whereby the'distance of travel of said, wiper from one terminal to another is uniform throughout the length of movement thereof, but whereby the wiper is given a variable number of steps between different terminals, metallic line circuits, and means ja to: sald trunk-lines, a wiper ad acent, s'a1 d terfor controlling the aforesaid operative elements over said metallic line circuits.

-17.' In a telephone system, a set of trunklines, bank terminals for said trunk-lines, a plunger adapted to travel back and forth in frontv ofsaidterminals, means for giving .said plunger a variable number of steps between difterent terminals, metallic'line circuits, and means for controlling the aforesaid operative elements over said metallic line' circuits.

18. In a telephone system, a plurality of trunk-lines, terminals for said trunk-lines, a traveling member adapted to move back and forth in front of said terminals, mechanism for giving the saidmcmber a step-by-step motion consisting of a series of successive steps: of variable lengths, metallic line circuits, and means for controlling the aforesaid operative elements over said metallic line circuits.

19. In a telephone system, a plurality of .trunk-lines,-an automatic switch for seizing idle trunklines, automatic K mechanism whereby a switching element of said switch isgiven a variable stcp-by-step motion, me-

itallicline circuits, and means for controlling the aforesaid operative elements over said metallic line circuits.

20. In a telephone system, a plurality of trunk-lines, terminals corresponding to said trunk-lines, said terminals bein uniformly spaced apart, a traveling mem er adapted to cooperate with said terminals, having a uniform distance of travel from one terminal ,to another throughout the range of travel thereof, mechanism for giving said traveling member a variable step-by-step motion between the different terminals metallic line circuits, and means for controlling the afore-.

-a=circuit-closing lunger adapted to travel along in front 0 said terminals, normally out of contact therewith, mechanism for giving said plunger a variable step-hy-step motion between the different terminals, metallic line circuits, and means for controlling the aforesaid operative elements over said metallic line circuits.

In a telephonesystem, a set of trunklines, a set of terminals corresponding to said.trunk-lines-, a wiper mounted to engage said terminals, mechanism for causing said wiperjto have a back and forth motion j tion to select groups or divisions of the ex Cri vided with notches at iri'egularinteri als n change, and rotary motion to extend connection from said trunk-lines in the direction of the called subscriber.

24. In a telephone system, a set of trunklines, a series of terminals corresponding to said trunk-lines, av'iper adjacent said terminals, means for moving said wiper back and forth over said terminals, means for causing said wiper to stop on idle terminals corresponding to trunk-lines in each direction ofmotion thereof, and automatic switches having vertical motion to select groupsor divisions of the exchange, and rotary motion to extend connection from said trunklines in the direction of the called subscriber.

In a telephone system, a set of trunla lines, a set of terminals corresponding to said trunk lines, a wiper adjacent said terminals, mechanism for moving the Wiper from one terminal to another, adapted to give the wiper a variable nuinberot' steps between terminals, but a uniform distance of travel from one terminal to: another, and automatic switches having vertical motion to select groups or divisions of the exchange, and rotary motion to extend connection from said trunk-lines in the direction of the called subscriber. I

26. In a telephone system, a set of trunkli'nes, a series of terminals corresponding to said trunk-lines, a wiper adjacent said terminals, a shaft upon which said wiper is mounted, an arm carried by said shaft and pivoted thereon to swing about an axis atright-angles to that of the shaft, a ratchet wheel engaging the free-end of said arm to move the same in a circle, a pawl for actuating said ratchet wheel, means for vary- .ing the number of teeth on the ratchet wheel engaged by said pawl in actuating the same to move the wipcr from one terminal to another, and automatic switches having vertical motion to select groups or divisions of the exchange, and rotary motion to extend connection trom'saidtrunlelines in the direction of the called subscriber.

27. In a telephone system, a set of trunklines, terminals corresponding to said trunklines, a shaft provided with a wipe adapted to eiigagesaid terminals. an arm pivoted on said shafttn swingaboutan axis at rightangles to the axis of the shaft. a ratchet wheel engaging the free end of said arm to move the same in a circle, and to there by move the said wiper back and forth over said terminals, a pawl engaging said ratchet wheel to actuate thee-Lime, a notched wheel rotating with the said 'ratclietclYheel, prothe periphery thereof, a magnet for operating said pawl,'means including circuit contacts engaging the periphery of said notched wheel to control the action of said magnet and pawl, whereby the distance of travel of said wiper from one terminal to another. is uniform throughout the length of movement thereof, but whereby the wiper is given a variable number of steps between differentterminals, and automatic switches-having vertical motion to select groups or divisions of the exchange, and rotary motion to extend connection from said trunk-lines in the direction of the called subscriber.

28. In a telephone system, a set of lIllIil-I- lines, bank terminals for said trunk-lines, a

plunger adapted to travel back and forth in" Qtkln a telephone system, a plurality of trunk-lines, terminals for said trunk linesfa traveling member adapted to move back and forth in front of said terminals, mechanism for giving the said member a step-by-step motion consisting of a series of successive steps of variable lengths, and automatic switches having vertical motion to select groups or divisions of the exchange, androtary motion to extend connection from said trunk-lines in the direction of the called subscriber.

30. In a telephone system, a plurality of trunk-lines, an automaticjswitch for seizing idle trunk-lines, -autoniatic mechanism whereby aswitching element of said switch is iven a variable s eed ste -bvste mo tion, and automatic switches having vertical motion to select groups or divisions of the exchange, and rotary motion to extend con"- nection from said trunlelines in the direction of the called subscriber.

31. In a telephone system, a plurality of trunk-lines, terminals corresponding to said trunk-lines, said terminals being uniformly spaced apart, a traveling member adapted to coiipe ate with said terminals, having a uniform distance of travel from one termi nal to another throughoutthe range of travel thereof, mechanism for giving said travel ing member a variable step-by-step motion between the different terminals, and automatic switches having. vertical motion to select groups ordivisions o the exchange, and rotary motion to extend connection from said trunk-lines in the direction of the called subscriber.

32. In a telephone system, a plurality of trunk-lines, terminals corresponding to said said terminals, mechanism for giving 'sa' wiper a variable speed step-by-step motion,

and automatic switches having vertical motion to select groups or divisions of theexchange, and rotary motion to extend connection from said trunk-lines in the direction of the called subscriber.

' 33. In a telephone system, a plurality of trunk-lineaterminals for said tru -lines,.a circuit-closing plunger adapted ,to travel along in front of said terminals, normally out of contact therewith, mechanism for giving said plunger a variable step-by-step motion between the diiferent terminals, and automatic switches having vertical motion to select groups or divisions of the exchange, and rotary motion to extend connection from said trunk-lines in the direction of the called subscriber.

3%. In a telephone system, a set of trunklines, terminals for said trunk-lines, sockets for said terminals, a plunger disposed in front of said sockets, mechanism operated to cause said plunger to travel back and forth in front of said sockets, with a step-by-step movement in each direction, to select an idle trunk ahead of the call, and means responsite to the calling subscriber for causing the Copies of this patent may be obtained for 1 iphinger to enter the socket at a preselected idle trunk-line. v

35. In a telephone system, a set of trunklines, terminal sockets for said trunk-lines,

each trunk-line having a plurality of said i sockets, plungers dis osedin'front of said sockets, mechanism or movin gers back and forth in front 0 said terminals, with a step-by step movement in'each direction, and instrumentalities whereby each calling subscriber causes one of saidplungers to enter the socket in front of which it was resting, and simultaneously therewith causes the other idle plungers to advance one way or the other to a position in front of the terminal sockets .of the next idle trunkline.

36. In a telephone exchange system, a master switch, and trunk terminals therefor, said switch including a switching element and means for moving said element step by step in opposite directions over the trun terminals, substantially as described.

Signed by me at Chicago, Cook county, Illinois, this 10th day of July, 1908.

ALEXANDER E. KEITH.

Witnesses J. No. $Y, F. H. DRURY.

five cents each, by addressing the Commissioner of Yatents,

! Washington, D. G.

said plun- 

